Bacteriophage lambda has been intensively studied by molecular biologists, and the results of these studies have been very interesting in terms of biology and very useful in developing powerful genetic engineering technologies. One of the less well understood aspects of lambda molecular biology is the nature of the control of the translational efficiency of its various genes. This is particularly clearly demonstrated in the late operon, in which translational efficiencies of different genes vary over 800-fold. Our preliminary studies have indicated that this control is exerted at the level of initiation of translation. We have proposed to study control of translation initiation in the lambda late operon in more detail, in particular with regard to (1) the contribution of nucleotide sequence per se to translational efficiency, (2) length of the Shine-Dalgarno sequence and its position relative to the initiation codon, (3) role of secondary structure, and (4) coupling to translation of the immediately upstream gene. These questions have not yet been satisfactorily answered in any system. Our choice of genes to study and experimental design should allow significant clarification of these questions regarding initiation of translation in prokaryotes, and in addition will contribute toward (1) our overall understanding of the molecular biology of the bacteriophage lambda life cycle and (2) design of vectors which overproduce proteins of choice in E. coli.